The invention is directed to a device switch for a hand-held tool, particularly for a screw drill or drilling machine, with a control device arranged in a switch housing, a trigger which is movably supported at the switch housing, the rotational speed of a driving motor of the hand-held tool being controlled by the control device depending on the position of the trigger relative to the switch housing, and a pressure increasing arrangement with a contacting element which makes pressing contact with a contact region of a mechanical resistance element in a center of pressure or trigger pressure position of the trigger between a zero load position and a full load position, the displacement resistance of the trigger being increased by this mechanical resistance element.
Hand-held tools of the type mentioned above make it possible for the user to press the trigger of the device switch initially only as far as the noticeable trigger pressure position even when there is a short displacement path of the trigger. In this position of the trigger, a workpiece can be pre-drilled at a relatively low rotational speed of the driving motor. As soon as the drill tip engages securely, the user can then actuate the trigger beyond the trigger pressure position by increasing pressing force on the trigger to continue the drilling process, e.g., at maximum speed of the driving motor. In this way, traditional center-punching of bore holes can be dispensed of when producing bore holes in metal or screwing to sensitive surfaces.
DE 30 16 488 discloses a device switch for a power tool in which a trigger has a contacting element in the form of an edge which comes into contact with a resistance element formed as a locking bushing along the movement path of the trigger. The locking bushing is held in the switch housing of the control device and is pressed by a pressure spring against a side of the trigger, which projects into the switch housing. When the edge and the locking bushing develop pressing contact, an appreciably increased pressure must be exerted on the trigger to push the edge of the trigger past the locking bushing to achieve an increase in the rotational speed of the driving motor.
A device switch of the type described above has the disadvantage that both the control device and the trigger must be specially shaped for setting up the trigger pressure position. In particular, the changes inside the switch housing require special authorization of the device switch and lead to very high production costs particularly in device series with relatively small piece numbers.
In addition, the known pressure increasing arrangement works not only in clockwise or clockwise rotation but also in counterclockwise rotation, which is troublesome rather than practical.